Using transgenic zebrafish that overexpress Myc, a central regulator of human T-cell acute lymphoblastic leukemia (T-ALL),[unreadable] we developed a zebrafish model of T-ALL with features that closely resemble the human disease. Here we[unreadable] propose to conduct the first modifier screen in a vertebrate system to identify both enhancers and suppressors of T-ALL[unreadable] in the zebrafish. We predict that enhancers of the T-ALL phenotype will represent mutations in genes that have tumor[unreadable] suppressor characteristics and that suppressors will be mutations in parallel pathways that inactivate genes required for[unreadable] transformation and thus encode candidate drug targets. The central hypothesis for this research is that mutations[unreadable] will be identified in zebrafish that accelerate or delay the onset of Myc-induced T-ALL, and that the roles of the[unreadable] genes affected by these mutations will be conserved in human T-ALL pathogehesis. One immediate goal will[unreadable] identify genes directly or indirectly involved in the molecular pathways of malignant transformation induced by Myc,[unreadable] lending insight into the molecular basis for T-ALL pathogenesis. An important long-term goal is to find potential gene[unreadable] targets and molecular pathways for the development of more specific and less toxic drugs for the treatment of T-ALL.[unreadable] These goals will be achieved through three specific aims. In Aims 1 and 2, we will perform a genetic modifier screen to[unreadable] identify and clone enhancer and suppressor mutations that affect the rate of onset of Myc-induced T-ALL. Since the[unreadable] zebrafish is transparent, the onset of leukemia can be observed as GFP-labeled T cells expand beyond the region of the[unreadable] thymus. During the previous grant cycle, we created separate transgenic zebrafish lines expressing TAL1, LM02, and[unreadable] EGFP-mMyc in T cells and have isolated a p53 mutant zebrafish line that is tumor prone. In Aim 1, we will also generate[unreadable] separate transgenic zebrafish lines with T-cell-specific expression of HOX11, HOX11L2, TAN1-EGFP, and mutated[unreadable] NOTCH11. We will test these transgenic and mutant lines, in addition to a panel of 315 retroviral insertional zebrafish[unreadable] lines (representing inactivating mutations in identified genes) generated by Dr Nancy Hopkins' lab, for modifiers of[unreadable] m/Wyc-induced onset of T-ALL. To achieve a more extensive coverage of the genome as well as to expand the[unreadable] spectrum of genomic mutational alterations, we propose in Aim 2 to perform an ENU-based Myc modifier screen, which[unreadable] will involve the random introduction of point mutations at a rate of approximately 100 inactivating mutations per genome.[unreadable] We have made major progress during the previous grant cycle in defining at least 5 multistep oncogenic pathways in T-ALL[unreadable] of children and adults. In Aim 3, we will determine the clinical consequences of these gene expression programs in[unreadable] childhood T-ALL and identify new proteins that can be targeted to develop highly specific therapies. The results should[unreadable] provide a new rationale for subclassifying patient groups at diagnosis, especially high-risk patients who may benefit from[unreadable] alternative therapies. Aim 3 will raise numerous opportunities to interact closely with other projects in this program with[unreadable] the ultimate goal of bringing novel targeted therapies to the bedside for children and adults with T-ALL. We are[unreadable] confident that the research outlined here will lead to the discovery of critical genes in the molecular pathways that drive[unreadable] T-ALL, which may provide novel targets for T-cell leukemia-specific therapies.